Allow kernel to set priority of processes.

Address the below denials:
type=1400 audit(1481886153.969:3726): avc: denied { setsched } for pid=20505
comm="kworker/2:8" scontext=u:r:kernel:s0 tcontext=u:r:system_app:s0 tclass=process permissive=0

Change-Id: I32e13e573c3918945bf52e40f537485c291f679f
CRs-Fixed: 1103022